Aspiration cytology of primary thyroid paraganglioma

Thyroid paragangliomas are extremely rare tumors arising from the inferior laryngeal paraganglia. Most patients are female and present as asymptomatic thyroid nodule. Diagnosing thyroid paraganglioma can be difficult on fine-needle aspiration (FNA) since it could be misdiagnosed as medullary thyroid carcinoma, calcitonin-negative neuroendocrine tumor of the thyroid gland (CNNETT), metastatic neuroendocrine tumor, and intrathyroid parathyroid proliferation. We describe the cytologic features and immunohistochemical staining pattern of thyroid paraganglioma from a 60-year-old woman with a gradually enlarging neck mass for several months. An ultrasound guided fine-needle aspiration was performed which revealed epithelioid, plasmacytoid to occasionally spindle-shaped cells with ovoid to elongated nuclei, fine chromatin pattern and inconspicuous nucleoli. The cells were arranged singly, in sheets, and focally in acinar pattern. Occasional nuclear overlapping, crush artifact, and binucleated cells were identified. Neither colloid nor amyloid was seen. Immunohistochemical stains performed on the cell block showed the tumor cells were positive for neuroendocrine markers and negative for cytokeratin (AE1/AE3), calcitonin, CEA, thyroglobulin, and TTF-1. There were rare S-100 positive cells. Given the difference in management of paragangliomas compared to its cytology mimics and association with familial cancer syndromes in some cases, awareness of this rare tumor, and use of immunohistochemical stains are critical in arriving at the diagnosis.